Polymer materials possess several properties which make them desirable for a large number of applications within fields such as hearing aid components, health care products, consumer electronics, toys, mobile phones, automotive components, etc. In such products it may be desirable to combine electrical and mechanical functions in a single component, for example to make electrical circuits directly on the cover or base of a polymer-based product. Such circuits may be made by means of positional selective metallization of desired areas.
In one type of metallization process, certain laser compatible particles are added to the polymer material before it is moulded. After the moulding, a laser beam is directed to the areas to be metalized to selectively expose these particles (this process is usually referred to as Laser Direct Structuring or LDS). A following electroless, or chemical, metallization may subsequently be performed on the surface of the exposed particles. This process is however expensive, since the entire polymer product is to be filled with particles although only the surface is used. Moreover, special particles and polymers are needed.
In an alternative process the entire surface may be metalized, and then in later process steps the unwanted metal areas are removed, e.g. by laser ablation, photo lithography followed by etching, etc. This method usually involves toxic chemicals in the pre-treatment, such as chromic acid. The method moreover often leads to a substantial waste of metal since most of the metal layers are removed.
U.S. Pat. No. 4,239,789 discloses a method for high resolution maskless electroless plating of an object. Preferential plating results from exposing those regions where plating is sought to an energy beam such as a laser, while the object to be plated is submerged in an electroless plating solution. The localised heating of the solution will speed up the chemical reaction leading to an increase of the plating rate by a factor of 103 to 104. This enhancement is sufficient to make masking unnecessary. However, the plating bath will still provide a plating film on unneeded positions on the object resulting in a waste of chemicals due to this lack of selectivity. Furthermore will the adhesion between the object to be plated and the deposited metal be relatively poor.
U.S. Pat. No. 4,659,587 aims to solve this selectivity problem by using the insight that when the object is heavily irradiated with e.g. a laser, an activation phenomenon appears in the irradiated areas of the object. The activation phenomenon supersede the need for preliminary activation before the actual plating takes place, and thus is activation not included in any of the examples mentioned in U.S. Pat. No. 4,659,587. The applied energy densities in the various examples of this reference are in the range from about 285 J/mm2 up to about 10,000 J/mm2 in order to obtain satisfactory metallization as measured by adhesion tests and profiling of the surface; FIG. 2. Thus, the object, typically a polymer, will be subjected to a quite intense energy absorption resulting in an inevitable burning or decomposition of the polymer object. This is also explicitly referred to as a “damaged area”. A further disadvantage is the fact that to deliver a sufficient laser energy, the laser scanning across the object is relatively low, i.e. in the order of 10-100 micrometer/second, which make industrial application of this method somewhat limited.
Hence, an improved method of selective metallization would be advantageous, and in particular a more cost-efficient, and/or less toxic method would be advantageous.